Why this happens

Ethernet and HDMI prove different things.

Ethernet works

The USB data path between host and hub is functioning.

Power delivery works

The charging path is functioning. This still says nothing definitive about display output.

HDMI fails

Now investigate the display path: host capability, upstream cable, dock mode, HDMI cable, and monitor input.

Step 01

Confirm the laptop's USB-C port actually outputs video.

Microsoft notes that a display adapter must be connected to a USB-C port that supports the correct Alternate Mode. Search the exact laptop model and read the specification for the port you are using. USB 3.2 data support alone is not evidence of DisplayPort output.

How to tell if the port supports video

Use the exact host specification and a direct display test instead of guessing from connector shape.

Step 02

Test video without the hub.

Connect a known-good USB-C monitor or a known-good USB-C-to-DisplayPort/HDMI adapter directly to the laptop. Keep the test simple: one display, one cable, no extension, no KVM.

  1. Direct video works.The host can output video. Move the diagnosis back to the hub/cable/HDMI path.
  2. Direct video fails.Re-check the host specification and try another documented video-capable USB-C port if the machine has one.

Step 03

If the hub has a removable upstream cable, replace that cable.

A cable can pass USB data while lacking the capabilities or signal integrity needed for the hub's display path. Use the cable supplied with the hub or one that meets the exact manufacturer requirement. Do not diagnose through a USB-C extension cable.

Step 04

Test the HDMI side as its own system.

  • Use an HDMI cable that you know works with another source.
  • Select the correct input manually on the monitor or TV.
  • Start at a conservative display mode such as 1080p at 60 Hz.
  • If possible, test the hub HDMI output on another known video-capable USB-C computer.

Decision

When you actually need different hardware.

Host has no video-capable USB-C port

A passive Alt Mode hub cannot create video. Use another native display output or a USB graphics solution designed for that purpose.

Direct video works, hub HDMI fails on multiple hosts

The hub HDMI path or upstream cable is the likely failure.

Hub works on another laptop

Compare the two hosts' USB-C display capabilities before replacing the hub.

USB-C dock compatibility

Choose a replacement based on the host rather than port count.

Second monitor breaks the dock setup

Continue if one display works and the failure starts only with display number two.

Sources

  1. Microsoft Support — Fix USB-C problems in Windows